Pidgin Delaware (also Delaware Jargon or Trader's Jargon) was a pidgin language that developed between speakers of Unami Delaware and Dutch traders and settlers on the Delaware River in the 1620s. The fur trade in the Middle Atlantic region led Europeans to interact with local native groups, and hence provided an impetus for the development of Pidgin Delaware. The Dutch were active in the fur trade beginning early in the seventeenth century, establishing trading posts in New Netherland, the name for the Dutch territory of the Middle Atlantic and exchanging trade goods for furs.

Pidgin languages characteristically arise from interactions between speakers of two or more languages who are not bilingual in the other group's language. Pidgin languages typically have greatly simplified syntax, a limited vocabulary, and are not learned as a first language by its speakers. Words typically have very general meanings but do not carry more than one meaning concept, and do not have the type of structural complexity commonly found in many languages.

Knowledge of Pidgin Delaware subsequently spread to speakers of Swedish, and later from Swedes to Englishmen, and was used beyond the immediate area where the pidgin originated. It is most likely that Swedes learned Pidgin Delaware from Dutch speakers; for examples, one of the early Swedish expeditions to the Delaware area had a Dutch interpreter. Similarly, succeeding English groups learned Pidgin from Swedes; Pennsylvania founder William Penn's interpreter Lars Petersson Crock was Swedish.

Pidgin Delaware was used by both Munsee and Unami Delawares in interactions with speakers of Dutch, Swedish, and English. Some non-Delaware users of the pidgin were under the impression that they were speaking true Delaware. Material cited by William Penn as being from a Delaware language is in fact from Delaware Pidgin, and he was apparently unaware of the difference between real Delaware and Pidgin Delaware.

Patterns of usage, involving both Munsee and Unami Delaware, as well as separate groups of Europeans, attests to a widespread and persistent use of Delaware Pidgin as a medium of communication for speakers of Dutch, Swedish, and English, as well as Unami- and Munsee-speaking Delawares.

Recordings of Pidgin Delaware suggest that Pidgin words originated from both Northern and Southern Unami. Although the best-known early Dutch settlement was New Netherland, on Manhattan Island, which is in Munsee Delaware territory, Pidgin Delaware has Unami vocabulary almost exclusively, with no terms that can be ascribed solely to Munsee. Even recordings of Pidgin Delaware that were clearly made in Munsee territory have Unami characteristics. The first permanent Dutch settlement in New Jersey was Fort Nassau (on the site of modern Gloucester City). Settlers to an earlier and short-lived factorij at Fort Wilhelmus arrived there in 1624 were subsequently removed to Manhattan between November 1626 and October 1628. Both of these locations are in traditional Unami Delaware territory. The origins of Delaware Pidgin must originate in the earliest contacts between Dutch settlers and Unami Delaware speakers at those locations.

The first recorded mention of Pidgin Delaware dates from 1628, while the final recorded mention is from 1785. There are two main sources of Pidgin Delaware material. Swedish Lutheran minister Johan Campanius, who served in New Sweden from 1642 to 1648, prepared a vocabulary list and translated into Delaware Pidgin a version of Martin Luther's Little Catechism, which was published after Campanius returned to Sweden. As well, an anonymous vocabulary list of some 260 words entitled "The Indian Interpreter" compiled in the late seventeenth century in West Jersey (an early British colony), and found in a book of land records from Salem County, New Jersey, also contains words in Delaware Jargon. There are also small amounts of material in several other sources, including a 1633 vocabulary collected by Joannis deLaet (de Laet's first name is often spelled inconsistently). Gabriel Thomas collected some Delaware Pidgin materials that were published in 1698. Another vocabulary collected by Ebenezer Denny in 1785 from Delawares who had migrated to western Pennsylvania has features of Pidgin Delaware.

Although Thomason has suggested on theoretical grounds that Pidgin Delaware predated the arrival of Europeans and was used for communication with speakers of Iroquoian languages, there is no attestation of its existence prior to European contact. Against this suggestion are references to the difficulty of communication between Delawares and Iroquoian speakers. Similarly, while Dutch recordings in this early period contain words in the Iroquoian language Mohawk, and Swedish documents contain words in Susquehannock, another Iroquoian language, the primary Dutch and Swedish recordings of interactions with Delawares reflect Pidgin Delaware, suggesting that these Europeans were not using Pidgin Delaware to communicate with Iroquoian speakers.